1. Field of the Invention
This invention relates to a printing apparatus and printing method for positioning the next printing area to the image formation unit after the last printing area of the previous printing instruction has been fixed, and more particularly to a printing apparatus and printing method for reducing wrinkling of the recording medium.
2. Description of the Related Art
Printing apparatus are widely used as output devices for computers. Electronic photographic devices, which are capable of printing on the normal paper, are used as such a printing device. In recent years, with the increase in speed and capacity of host systems, electronic photographic printing devices that are capable of printing large quantities of data at high speed are desired. Therefore, electronic photographic printing devices that print on continuous paper, which can be continuously fed, are being provided.
FIG. 33 is a drawing explaining the prior art. Is shows an electronic photographic type, continuous-paper printing device. In the electronic photographic printing device, a toner image, that is developed on the photoconductive drum, is transferred to the paper, then the transferred toner image is fixed and the printing process is finished.
This electronic photographic type continuous-paper printing device is explained for a printing device that prints both surfaces of the paper. As shown in FIG. 33, the double-side printing device comprises: a printing unit 101 that prints the top surface of continuous paper 100, and a printing unit 102 that prints the back surface of the continuous paper 100. The continuous paper 100 has machine perforations on every page. The printing unit 102 for the back surface has a photoconductive drum 90. The photoconductive drum 90 is electrically charged by a pre-charger that is not shown in the drawing, then it is exposed with the light image by an exposure device that is not shown in the drawing. By doing this, an electric latent image that corresponds to the light image is formed on the photoconductive drum 90. And the electric latent image on this photoconductive drum 90 is developed by toners with a developing device that is not shown in this figure. And then the toner image on this photoconductive drum 90 is transferred to the continuous paper 100 by a transfer device 91. Printing the back surface of the continuous paper 100 is performed in this way.
The top surface of the continuous paper 100 is printed in a similar manner. In other words, the printing unit 101 for the top surface also has a photoconductive drum 92. The photoconductive drum 92 is electrically charged by a pre-charger (not shown in the drawing), and then is exposed with light image by an exposure device that is not shown in the drawing. By doing this, an electric latent image that corresponds to the light image is formed on the photoconductive drum 92. And the electric latent image on this photoconductive drum 92 are developed by toners with a developing device not shown in this figure. And then the toner image on this photosensitive drum 92 is transferred to the continuous paper 100 by a transfer unit 93. Printing the top surface of the continuous paper 100 is performed in this way.
Next, the toner images on both surface of the paper 100 are fixed by a fixing unit 94. This fixing unit 94 uses various methods for fixing the toner. For example, there is a heat-roller method that moves the paper with a high-temperature heat roller and fixes the toner with heat, or there is a flash fixing method that uses a flash lamp to irradiate the paper with a high-energy light that melts and fixes the toner. This kind of electric photographic type double-side printing device for printing on continuous paper has been discloses in Japanese Unexamined published patent No. 7-77581, or Japanese Unexamined published patent No. 8-211664.
With this kind of continuous-paper printing device, the transfer position of the toner image and the fixing position are separated. Therefore, if the last printed page 110 of one printing job stops in an un-fixed state when one printing job is finished printing, the un-fixed image could be blurred due to various causes. Therefore, when a xe2x80x98Stop Printingxe2x80x99 command is received, it is not advisable to stop feeding paper when there are still unfixed pages.
Therefore, before printing operation is stopped, the transferred pages are fed and fixed by the fixing unit 94. In other words, the last printed page 110 of the job is positioned in fixing unit 94. At this time, the next page 111 after the last printed page 110 is positioned very near the fixing unit 94. When printing starts from this state when the next printing job arrives, not the next page 111, but a page area 2 to 3 pages later is positioned in the image forming unit 102, so the space between the next page 111 and this page area is not printed and becomes a blank page. This is a waste of paper.
As shown by the arrows in the figure, in order to do away with this blank page, after the last printed page 110 has been fixed by the fixing unit 94, it is proposed to feed the paper backward at the start of the next job to a position where the image forming unit 102 can transfer an image to the next page 111.
FIG. 34 is a drawing explaining the problems with the prior art. In the fixation step such as flash-light, the flash light is flashed on the un-fixed toner, and the toner is melted by the heat and fixed. When doing this, the moisture in the paper (continuous paper) 100 is evaporated, and this dries the paper and causes it to shrink. As shown in FIG. 34, in the aforementioned printing operation sequence, the last page 110 of the previous printing has shrunk considerably by fixation, and the first page 111 of the next printing has not shrunk at all.
When a paper shrinkage difference occurs between these adjacent pages, since originally the paper was continuous paper with the same width, the paper with the width is pulled by the paper with the narrow width, and wrinkling in the shape of a sine curve occurs in the vertical direction. In other words, wrinkling occurs at the top of the first page 111 of the next printing.
Printing is then performed on this wrinkled starting page 111, and when the toner image is transferred to the page by the image formation unit, not all of the page in the width direction of the paper comes in uniform contact with the photo-sensitive drum, so there is a problem in that there are areas where no toner is transferred.
Particularly, in the case of a high-speed printer (for example when printing at 8000 lines/min.), the speed at which the continuous paper is moving is fast and the transfer time is short. Therefore, there is a good chance that toner will not be transferred to the areas of no contact due to the wrinkling.
Moreover, in a double-side printing device, fixation energy is applied from both side of the paper by the fixation unit, so there is a large amount of moisture that evaporates from the paper. Therefore, there is a large amount of paper shrinkage, and it becomes easy for wrinkling to occur in the first page.
The objective of this invention is to provide a printing device and printing method for reducing the amount of wrinkling that occurs in the leading region of the record medium, and preventing poor toner transfer to this leading region.
Another objective of the invention is to provide a printing device and printing method, for reducing the amount of wrinkling that occurs in the leading region of the record medium and preventing poor toner transfer to this leading region, which is simply constructed.
A further objective of the invention is to provide a printing device and printing method for reducing the amount of wrinkling that occurs in the leading region of the record medium and preventing poor toner transfer to this leading region, in which it is possible to adjust the amount of moisture evaporation in the end region.
Still a further objective of the invention is to provide a printing device and printing method for reducing the amount of wrinkling that occurs in the leading region of the record medium and preventing poor toner transfer to this leading region, in which it is possible to adjust the amount of moisture evaporation in the leading region.
Yet another objective of the invention is to provide a printing device and printing method for selectively preventing poor toner transfer to the leading region of the record medium due to wrinkling of the leading region.
Even yet a further objective of the invention is to provide a printing device and printing method for automatically detecting the occurrence of wrinkling in the leading region of the record medium that may affect the transfer of toner, and for selectively preventing poor toner transfer to this leading region due to wrinkling.
In order to accomplish the objectives of the invention, the printing method of this invention comprises: an image formation step of transferring a toner image to a continuous record medium by an image formation unit; a fixation step of fixing the toner image on the record medium; a step of adjusting the amount of moisture of the record medium for reducing the difference in the amount of shrinkage between a final printing area of the record medium of a previous printing instruction and a next printing area after the final printing area; and a step of positioning the next printing area at the image formation unit after fixation of the final printing area of the previous printing instruction has been completed.
Moreover, the printing device of this invention comprises: an image formation unit for transferring a toner image to a continuous record medium; a fixation unit for fixing the toner image to the record medium; and adjusting means for adjusting the amount of moisture of the record medium for reducing the difference in the amount of shrinkage between the final printing area of the record medium of the previous printing instruction and the next printing area after the final printing area.
In this form of the invention, there is a step or means of adjusting the amount of moisture of the record medium for reducing the difference in the amount of shrinkage between the final printing area of the record medium of the previous printing instruction and the next printing area after the final printing area, so it is possible to reduce the difference in the amount of shrinkage between the final printing area and the next printing area, and thus it is possible to reduce the occurrence of wrinkling in the leading area of the next printing instruction. This makes it possible to prevent poor toner transfer to the leading area of the next printing instruction.
The printing device of another feature of this invention comprises: a feeding unit for feeding the continuous record medium; an image formation unit for transferring a toner image to the record medium; a fixation unit for fixing the toner image to the record medium; and a control unit for controlling the feeding unit in order to position the next printing area on the record medium following the final printed area after the final printing area on the record medium of the previous printing instruction has been fixed.
In one form of the invention, the control unit controls the fixation unit such that fixation energy of the fixation unit for the final printing area is less than the fixation energy for area other than the final printing area.
In this form of the invention, since the fixation energy at the final printing area is reduced, it is possible to reduce the amount of moisture evaporation at the final printing area. Therefore, it is possible to reduce the amount of shrinkage of the final printing area, and lessen the amount of wrinkling of the leading area for the next printing instruction. This makes it possible to prevent poor toner transfer at the leading area for the next printing instruction.
In the printing device of another form of the invention, the control unit further controls the fixation unit such that it applies fixation energy to the final printing area at the start of the next printing instruction. In this form of the invention, since the fixation energy at the final printing area has been lowered, fixation occurs, but is not complete fixation. Therefore, fixation energy is applied to the final printing area at the start of the next printing instruction to complete fixation. In this case, fixation is performed at the start of the next printing instruction, and toner is transferred to the leading printing area. Therefore, poor toner transfer to the leading printing area does not occur, even when fixation energy is applied to the final printing area.
In the printing device of another form of the invention, the control unit controls the feeding unit so that after fixation energy is applied by the fixation unit to the next printing area following the final printing area, the next printing area is positioned at the image formation unit.
In this form of the invention, since fixation energy is applied to the next printing area in advance, a certain amount of moisture is evaporated from the unprinted next printing area. Therefore, the next printing area shrinks a little, and the difference in shrinkage with that of the final of printing area becomes small, and the occurrence of wrinkling of the leading area for the next printing instruction is reduced. This makes it possible to prevent poor toner transfer to the leading area for the next printing instruction.
The printing device of another form of the invention comprises a moisture adjustment means for reducing the amount of moisture in the record medium of the next printing area. In this form of the invention, since the amount of moisture of the next printing area is reduced, the next printing area is shrunk a certain extent. Therefore, the difference in shrinkage with that of the final printing area becomes small, and the occurrence of wrinkling of the leading area for the next printing instruction is reduced. This makes it possible to prevent poor toner transfer to the leading area for the next printing instruction.
In the printing device of another form of the invention, by further having a selection-control unit for selectively operating the moisture-adjustment means, the wrinkle smoothing operation is not executed when there is no effect on toner transfer to the next page, so it is possible to keep any drop in the printing speed to a minimum.
Moreover, in the printing device of another form of the invention, the selection-control unit comprises a selection-control unit for detecting the printing dot distribution of the final printing area, and selectively operating the moisture-adjustment means, so it is possible to easily detect occurrence of wrinkling on the next page and whether there will be any effect on toner transfer.
Furthermore, in the printing device of yet another form of the invention, the selection-control means calculates the printing rate for each division of the final printing area that has been divided from the printing data of the final printing area, calculates the wrinkling value from the coefficients of the aforementioned printing rate, sub-scanning direction and main scanning direction, and determines where to selectively operated the moisture-adjustment means, thus it is possible to accurately detect the occurrence of wrinkling of the next page.